The consumption of traditional sources of energy continues to increase exponentially. This has burdened millions of people and nearly every nation with the task of supplying and maintaining fossil fuels to feed everything from home electricity to industry to transportation. This situation has proven costly in terms of supply as well as environmentally. Because of this, development of alternative sources of energy is crucial. However, there is a need for alternative sources of energy that conform with not only the energy needs of the population, but also other extraneous needs such as aesthetics, efficiency and convenience.
Renewable energy sources have the most potential for providing an efficient and economically viable alternative. Wind energy is the fastest growing energy technology in the world. The importance of realizing sustainable energy sources that are both economically viable as well as environmentally safe is evident but certainly no easy goal to fulfill. Innovative technological improvements of wind-turbine design have the potential to lower the cost of energy well below the U.S. government proposed $0.025/kWhr within the next few years.
While variations of wind turbines certainly exist, there continues to be a need for turbine blades that are both aerodynamic and quiet. Almost all large wind turbines built today have pitch bearings at the blade root so that the pitch of the whole blade can easily be changed by activating the pitch mechanism. Pitching of the blade is used as a brake to stop the rotor, but it is also used for power and load control in different ways. On active stall controlled turbines, a relative slow variation of the pitch of the blades is used to adjust the pitch so that stall on the blade occurs at the right maximum power. But pitch also is active at low wind speed to maximize the power. On pitch controlled wind turbines, the pitch at high wind is changed continuously so that the maximum power is not exceeded. This is done by reducing the inflow angle to the blade when the wind speed is increasing. The pitch also is used at low wind speeds to maximize the power. Recently, new types of pitch regulated wind turbines also use the pitch system to reduce the dynamic loads, either by cyclic pitch or by individual blade pitch. Different input signals to the control system such as flap-wise loading can be used. While the pitch adjustments for the entire turbine blade have shown some effect, there remains a need to increase upon those early advances in a manner that is even more efficient and also quieter. The present invention satisfies this need by appending a tip device and various sensors and controls that serve to either passively or actively adjust only the pitch of the tip device rather than the entire turbine blade. By conducting the process in this manner, the present invention presents a more efficient system that has the important additional benefit of reduced noise signature.
Apart from the above existing control with blade pitching, control of power and loads by movable, small control surfaces are available. Among them there is a partial span aileron system for control of power and rotor rotational speed. The aileron system is similar to trailing-edge flaps for airplanes. Gurney flaps attached to the trailing edge of the blades have as well been proposed and analyzed. The advantage of a small control surface is a possible faster response due to less inertia than if the whole blade is being pitched. One disadvantage of Gurney flaps, however, is the increase in aerodynamic noise from the free ends of the Gurney flaps and from the gaps in the blade where the Gurney flap is positioned. The present invention, in contrast, solves this noise problem by controlling the pitch angle of the tip device so that the flow passes through its cylinder in a manner that reduces noise.
The proposed flow control devices installed at the blade tip of the present invention can operate in passive, active or hybrid mode. As opposed to available active rotor control and passive control usually only suitable to large wind turbines, the present invention is suitable to a variety of wind turbines ranging from small to large. The tip device produces an aerodynamic flow jet that will improve the performance of the blade tip aerodynamics contributing to the overall performance of the wind turbine.